This invention relates to the combined fields of air supply systems which supply pressurized air to spray gun equipment and control devices to control the flow of such pressurized air. It relates in particular to an air supply and control assembly which provides a high volume low pressure (HVLP) supply of pressurized air and control means coupled therewith.
Prior art spray equipment has utilized pressurized air at relatively high air pressure with little thought that for a number of applications a lower pressure of air and a relatively higher volume of air would do a superior job. In recent years, it has been recognized that it is not enough to merely connect spray equipment to an air compressor or other pressurized air source, but that some method of increasing the volume of air flow per time unit and lowering the air pressure per square inch or other dimensional measurement is desirable. A number of high volume, low pressure (HVLP) air supply devices and air spray devices have been proposed and offered in recent years, often with less than satisfactory results.
The air supply and control assembly in accordance with the present invention is an improvement over the prior art and includes (A) an improved high volume, low pressure (HVLP) air supply component in combination with (B) a control component which couples a first source of pressurized air (for controlling operation of the needle valve and liquid output from the orifice of a spray gun) to a second source of pressurized air (for atomizing the output from the spray gun) to, by such coupling, control the flow of the second source of pressurized air to the atomizing component of the spray gun.
Such control of the flow of atomizing air to the spray gun includes (1) simultaneous flow thereof as soon as the first source of pressurized air is flowed to the spray gun to open its needle valve for flow of liquid to be atomized and sprayed so that atomizing air from the spray gun is available to atomize and spray the liquid as soon as it begins to flow from the nozzle orifice of the spray gun, (2) shutting off the flow of pressurized air from the second source after pressurized air from the first source has been shut off, and (3) delaying shut off of the flow of pressurized air from the second source for a predetermined time after pressurized air from the first source has been shut off to be sure that atomizing air is still being emitted from the spray gun to atomize and spray any liquid that may continue to flow from the spray gun orifice after the first source of pressurized air is shut off (signalling the needle valve to close the nozzle orifice) and the time it takes thereafter for the needle valve to fully seat in and fully close the nozzle orifice.
The present invention thus solves a problem of prior art devices and prevents an unintended stream of non-atomized liquid from flowing out of the spray gun when it has been signaled to discontinue its operation. Any such stream of non-atomized liquid on to the work pieces ruin such work and require rejection of those work pieces.
The HVLP air supply component of the present invention includes a venturi member which receives pressurized air from the second source into and through a venturi nozzle whose outlet is centered in the outwardly flared throat portion of an elongated cylindrical venturi member. A rearward portion of the elongated venturi member adjacent to the throat section on its upstream side includes a plurality of radially spaced apart apertures extending through its cylindrical wall and opening to its central passageway at a point adjacent to and slightly upstream from the narrowed neck portion and downstream outlet of the venturi nozzle, to draw ambient air therein through an air filter mounted in and through the wall of a sleeve member surrounding the rearward portion of the elongated venturi member. The ambient air drawn into the venturi member and pressurized air from the second source provides a supply of high volume low pressure (HVLP) atomizing air to the atomizing component of the spray gun.
The control component of the present invention comprises a coupling assembly to couple the first source of pressurized air (which controls operation of the needle valve of a spray gun) to a pilot valve which is connected to the second source of pressurized air (which controls supply thereof to the atomizing component of the spray gun). The coupling assembly includes a manifold which has one port connected to the first source of pressurized air, a second port connected to the piston and cylinder component of the spray gun which operates the needle valve, and a third port connected to a coupling passageway which is connected to a pilot valve.
The pilot valve includes an air chamber to receive pressurized air from the first source therein from the manifold and through the coupling passageway. The pilot valve includes a valve operator to move its valve closure member from an air flow closed position to which it is normally biased to its air flow open position when air pressure from the first source enters the air chamber of the pilot valve. Pressurized air from the second source can then flow through the pilot valve and through the venturi member connected to the pilot valve to supply high volume low pressure (HVLP) atomizing air to the atomizing component of the spray gun.
A control center, such as a computerized control assembly, controls the operation of the first source of pressurized air. When the control center wants to start a spraying operation it opens the flow of pressurized air from the first source which flows through the ports of the manifold to initiate both the flow of liquid from the spray gun nozzle orifice and atomizing air from the atomizing component of the spray gun. When the control center decides to stop a spraying operation, it closes the flow of pressurized air from the first source. The needle valve of the spray gun is then no longer pressurized to its valve open position whereupon biasing means biases it back toward its valve closed position. At the same time, pressurized air from the first source in the air chamber of the pilot valve begins to escape therefrom, after which the closure member of the pilot valve is biased to its closed position to cut off further flow of pressurized air from the second source to the atomizing component of the spray gun.
To provide the desired time delay in shutting off atomizing air to the spray gun until a certain amount of time has elapsed after shutting off the flow of pressurized air from the first source to the needle valve operating component of the spray gun, a check valve is provided in the coupling passageway. When a spraying operation is to start, the check valve allows first source pressurized air to flow freely to the chamber of the pilot valve enabling it to open immediately to begin flow of atomizing air to the spray gun. However, the check valve impedes return flow of the first source pressurized air out from the pilot valve chamber back to the manifold after that first source of pressurized air to the manifold has been shut off by the control center to discontinue the spraying operation. The longer such return flow of first source pressurized air from the pilot valve chamber is impeded, the longer it will stay open to continue supply of atomizing air to the spray gun.
The check valve is adjustable so as to vary the return flow of first source pressurized air from the air chamber of the pilot valve and thus the length of time the pilot valve remains open and the length of time atomizing air will continue to flow out from the spray gun after the first source of pressurized air has been shut off signalling the needle valve of the spray gun to close.
In order to make the rate of air flow in the coupling passageway more uniform and predictable, an enlarged capacity accumulator chamber is connected in the coupling passageway between the check valve and the pilot valve. As pressurized air from the first source flows into and through the coupling passageway to the pilot valve, the accumulator chamber fills with pressurized air. When pressurized air from the first source is shut off and return flow from the air chamber of the pilot valve begins, pressurized air from the accumulator chamber also flows into the coupling passageway and toward the manifold thus joining air from the air chamber of the pilot valve in its return flow back toward the manifold thus insuring a more uniform rate of flow. The time delay for any particular setting of the check valve can thus be predicted and determined more accurately, and more uniformly for each repeated operation.
A more complete description of the manifold, check valve, pilot valve, accumulator chamber and venturi is set forth hereinbelow and as illustrated in the accompanying drawings.